1. Field of Application
The present invention relates to a method for producing a thin film head which is used in magnetic disk units.
2. Prior Art
FIG. 1 is a plan view showing an exterior view of a conventional thin film head. In FIG. 1, There is a wafer (1) and an upper core.(2). At the front end of the upper core (2), an upper pole (2a) is formed. A coil (3) is connected at both ends to pad sections (4, 4).
FIG. 2 contains sectional views showing processes for producing the thin film head. These sectional views show the opposing faces of the upper and lower poles (FIG. 1) that face a recording medium (disk). The following describes the processes for producing the thin film head.
[1] First, a lower core (5) is formed on the surface of a wafer (1) by forming a permalloy (NiFe) into a rectangular shape by sputtering or vacuum deposition (See FIG. 2a). In FIG. 2, the symbol 2a designates the lower pole.
[2] Next, a gap layer (6) is formed by laminating alumina (Al.sub.2 O.sub.3) so as to coat the lower core (5) by sputtering. (See FIG. 2b).
[3] Then, a coil (3) is formed above the lower core (5) (See FIG. 1.). In this case, the coil (3) is coated with an insulation layer (not shown) so that the coil (3) does not contact the lower core (5) and upper core 2 which is formed in a later process.
[4] Next, a plating base (7) is formed by laminating a permalloy on the surface of the gap layer (6) by means of sputtering (See FIG. 2c.).
[5] After forming the plating base (7), resist frames (8 and 9) for plating the upper core with a rectangular shape are formed on both sides of the lower core as shown in FIG. 2d.
[6] Then, a permalloy is laminated on the surface of the plating base (7) by electroplating. (See FIG. 2e.) This forms an upper core (2) between the resist frames (8 and 9). In FIG. 2, the symbol 2a designates an upper pole. The width of the portion where the lower core (5) faces the upper core (2) through the gap layer (6) is the track width, Tw (that is, the width of poles 2a and 5a).
[7] After forming the upper core (2), the resist frames (8 and 9) are removed by using a remover (solvent) (See FIG. 2f.).
[8] Next, the exposed plating base which was covered by the resist frames is removed by ion miling (See FIG. 2g.). This almost completes the formation of the head.
[9] After finishing the above-mentioned process, a resist mask (10) is formed on the core section to coat the upper core (2) by photolithography (See FIG. 2h.).
[10] Next, all parts not to be included in the head are removed by etching. (See FIG. 2i.)
[11] Finally, the resist mask (10) on the core section is removed by means of a remover (solvent) (See FIG. 2j.).
Above is a description of the processes for producing a thin film head. However, the above-constructed thin film head has the following disadvantages. When the resist frames (8 and 9) are formed to plate the upper core (see FIG. 2d), the upper and lower cores often go out of alignment. For example, as shown in FIG. 3, when the resist frame (9) is positioned to the right apart from the lower core (5), the upper core (2) is positioned off to the right, as shown in FIG. 4.
Furthermore, the exposure device easily goes out of focus when aligning partly because the wafer (1) already has many surface level gradations on its contact surface with the coil and pad. For example, if a wider area than the set track width is exposed, the resist frames (8 and 9) for plating the upper core are formed apart from both sectional sides of the lower core, as shown in FIG. 5. Consequently, the upper core formed is wider than the lower core. To prevent this, exposure may be made narrower than the actual width to allow for the lack of focus. In this case, however, resist frames 8b and 9b for plating the upper core may be formed with a distance between them that is narrower than the width of the lower core, as is shown in FIG. 7. Consequently, the upper core formed may be narrower than the lower core.
Above is a description of the disadvantages of using a known method for producing thin film heads. The method is very susceptible to out-of-alignment and out-of-focus resulting in the formation of the upper and lower cores of different width as shown in FIGS. 4, 6 and 8. If the width of the upper core is narrower than that of the lower core and the track width Tw is narrower than the set value, the regeneration output level is lower. On the other hand, a possible surplus part outside the track width Tw may come in contact with an adjacent track and cause cross-talk.
Another way to form the head is shown in FIG. 9. In this method, ion-milling is performed after forming the upper core (14) on the gap (12) narrower than the lower core (13) (refer to Publication of unexamined Japanese patent application No. Tokukaisho 63-55711 (1988)). As shown in FIG. 10, when ion-milling is conducted, an ion beam (e.g. cation argon) collides against the lower core (13) and scatters magnetic materials which adhere to the side of the upper core (14). This magnetically shorts the upper and lower cores (13 and 14), as shown in FIG. 11. The magnetic shortcircuiting of the upper and lower cores (13 and 14) significantly reduces the read/write efficiency of the head.